The measurement of electric fields existing in open space is of importance for many industrial and meteorological purposes. One type of instrument which performs this function is known as a "generating voltmeter" or "field mill". In this type of instrument one metallic plate is alternately exposed and shielded from the field by a grounded metallic rotor. The resulting fluctuating charge on the stationary metallic plate flows to ground through a resistor thereby producing an electrical output signal that is related to the electric field being measured. A number of variants of this basic idea have been developed. For example, the required fluctuating shielding action can be effected with a suitably designed tuning fork mechanism to remove the need for a rotational drive for the grounded metallic rotor. Such schemes have depended basically on some periodic and relatively large scale mechanical motion to vary the coupling of the electric field of interest to a pickup electrode. As such they comprise field sensing devices that involve mechanical transducers, thereby limiting their usefulness for some applications where methods requiring no moving parts could possess significant advantages.